Davis - Blogs | Blog | Q&A: What is carbon sequestration?

2 Mar

With Paul Hepperly’s upcoming lecture on sustainable farming’s ability to lower greenhouse gases, we thought it would be a good opportunity to provide some basic information on a term that’s widely used but maybe not so widely understood: “carbon sequestration.” Mark Sperow, an Associate Professor of Agricultural and Resource Economics, researches land uses and their impact on the accumulation of greenhouse gases. We asked Professor Sperow to provide a lesson on Carbon Sequestration 101. Here’s what Professor Sperow had to say:

Background

Carbon dioxide enters the atmosphere when fossil fuels such as coal and petroleum are used to produce energy (electricity, transportation, etc.). The Environmental Protection Agency estimates that fossil fuel combustion in the U.S. released 5,657 million metric tons of carbon dioxide into the atmosphere in 2004 (about 94% of carbon dioxide emissions from all sources) (US-EPA, 2006). These carbon dioxide emissions represent a 20.4% increase over the emissions in 1990 and a 754% increase over the carbon dioxide emissions in 1900 (US-EPA, 2006; Marland et al., 2008). The primary source of carbon dioxide emissions early in the 20th century was from clearing forests for development and plowing soils for agricultural production.

Carbon dioxide, methane, nitrous oxide, flurocarbons, and halocarbons are greenhouse gases which trap heat from the sun on the earth’s surface. The most significant greenhouse gas, representing over 64% of all greenhouse gas emissions, is carbon dioxide. While a natural level of atmospheric greenhouse gases is necessary to maintain the earth’s surface temperature, there is concern over the consequences of the level and rate of increased carbon dioxide in the atmosphere.

1. What exactly is “carbon sequestration”?

Emissions of carbon dioxide may either be reduced directly by using alternative production processes, including alternative fuel sources, or they may be offset through carbon sequestration. A ton of sequestered carbon dioxide offsets a ton of emitted carbon dioxide, so there is no net increase in atmospheric carbon dioxide levels. Carbon sequestration is the storage of carbon dioxide in various geologic or terrestrial “sinks” where it is prevented from entering or reentering the atmosphere.

Geologic carbon sequestration involves capturing the carbon dioxide at the source before it enters the atmosphere, compressing it, and then injecting it into a geologic formation for permanent storage. The most likely sites for geologic carbon sequestration are depleted oil and gas reservoirs, deep saline formations (porous rock saturated with brine), unmineable coal seams (coal seams too narrow and deep to remove), and basalt formations (solidified lava) with the pore space and geologic characteristics necessary for permanent storage. Most current research is directed toward deep saline formations which scientists estimate could store 3,300 to 12,200 billion metric tons of carbon dioxide (US-DOE, 2008).

Just as the atmosphere holds carbon dioxide, terrestrial systems also hold a large amount of carbon dioxide in vegetation, soils, and oceans. Globally, the carbon dioxide stored in vegetation, soils (as carbon), and oceans is about 77%, 208%, and 5,278% of the atmospheric level of carbon dioxide respectively. Plants use carbon dioxide that is drawn from the atmosphere and oceans absorb carbon dioxide. A portion of the carbon dioxide used by plants and absorbed by oceans is returned to the atmosphere through natural processes. This process of removing carbon dioxide from the atmosphere and the return of a portion of the carbon dioxide back to the atmosphere is called the carbon cycle. The goal of terrestrial carbon sequestration is to increase the amount of carbon dioxide removed from the atmosphere and permanently store it in soils and vegetation, thus preventing its return to the atmosphere. Terrestrial carbon sequestration uses this natural carbon cycle to increase the amount of carbon dioxide stored in biomass by increasing “permanent” vegetative cover (forest, grassland, etc.) and decreasing the carbon losses from soils and vegetation. Vegetation removes carbon dioxide from the atmosphere through photosynthesis. A portion of the carbon dioxide ends up in root systems, which adds to the amount of soil carbon as they die. Increased carbon in the soil not only offsets carbon dioxide emissions from other sources, but it has the benefit of increasing the water holding capacity of soils and enhancing nutrient availability. Agricultural soils in the U.S. have the potential to store 75 – 208 million metric tons of carbon (equivalent to 275 – 763 million metric tons of carbon dioxide) each year given appropriate land management activities (Lal et al., 1998). Forests currently store about 200 million metric tons of carbon (733 million metric tons of carbon dioxide) each year, which could be increased by 100 – 200 million metric tons (367 – 763 million metric tons of carbon dioxide) with proper management (Birdsey, 2006).

2. What are some of the ways we can “capture” carbon dioxide from the atmosphere?

Forest land
Forests store carbon in the above-ground vegetation, the litter layer of leaves, and in soils. Planting new forests and managing existing forests effectively increases stored carbon.

Agricultural land (cropland, grassland, rangeland)
Soil characteristics, climate, land use, land use change, and management activities control the amount of carbon stored in soils. How the land is used (cropland, forest, urban, etc.) influences the amount of carbon that may be stored in soils. Conversion of land from one land use to another, for example from forest to cropland, also influences the amount of stored carbon (either losses or gains, depending on the change).

There are several ways to increase the amount of stored carbon on agricultural land. Plowing, tilling, and other activities that disturb the soil surface release carbon back into the atmosphere from agricultural land. Changing production systems from intensive tillage to no-till operations decreases soil disturbance and allows for increases in the amount of stored carbon. Improved cropping systems such as increasing the efficiency of fertilizer use or application of organic manures and by-products can increase stored soil carbon. Converting marginal cropland, particularly land identified as highly erodible, to native vegetation (grass or forest) provides significant increases in soil carbon. In some parts of the country, it is possible to include a winter cover crop in a crop rotation, which increases the biomass inputs and consequently enhances carbon sequestration. On pastures it is possible to increase stored carbon changing the way livestock are grazed, using improved plant species, including legumes in the plant mix, and using fertilizer efficiently.

3. What kind of research is going on at WVU that addresses carbon sequestration?

Researchers at WVU are analyzing the soil carbon sequestration potential on reclaimed mineland, from organic farming activities, and from other agricultural land management activities. In addition, there are research activities to assess potential carbon sequestration in forest biomass, soils, and litter layer. Researchers are also analyzing the economic consequences of marketable carbon dioxide offsets by assessing potential income that may be available to landowners from activities that increase terrestrial carbon sequestration.

References

Birdsey, R., K. Pregitzer, and JA. Lucier. 2006. Forest Carbon Management in the United States: 1600-2100. J. Envron. Qual. 35: 1461-1469.

Lal, R., J.M. Kimple, R.F. Follett, and C.V. Cole. 1998. The Potential of U.S. Cropland to Sequester Carbon and Mitigate the Greenhouse Effect. Sleeping Bear Press, Ann Arbor, MI, 128 pp.

Marland, G., B. Andres, and T. Boden. 2008. Global Carbon Dioxide Emissions from Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-2005. Available at http://cdiac.ornl.gov/ftp/ndp030/global.1751_2005.ems, accessed 25 February 2009.